A lean burn engine includes an autothermal reactor which receives a hydrocarbon feed from which a hydrogen-rich gas is to be generated together with air (or an oxygen-containing gas) and steam. The hydrocarbon feed may be preheated to a temperature of about 200 to about 900° C. and is fed into the autothermal reactor which is typically maintained at a temperature of about 250 to about 1100° C.
The autothermal reactor contains a layered catalyst member which initiates and sustains both catalytic partial oxidation and steam reforming reactions. The hydrocarbon feed may consist of C5 and heavier hydrocarbons, but is preferably a normally gaseous or readily vaporizable hydrocarbon such as a C1-C4 alkane, e.g., methane, propane, butane, etc. The amounts of the hydrocarbon feed, steam, and air introduced into the autothermal reactor may further be controlled by other components in the system.
During operation, the autothermal reactor may get relatively hotter at an inlet face thereof due to net exothermic reactions (i.e., combustion) exceeding net endothermic reactions (i.e., steam reforming). Further, sometimes the inlet stream may contain sulfur. In this case, the high temperatures at the inlet face may be exacerbated in the presence of sulfur, as sulfur suppresses the combustion reaction less than the steam reforming reactions. Due to this difference in temperature along a length of the autothermal reactor, the life of the autothermal reactor may be affected since the catalyst at the inlet face of the autothermal reactor may age relatively quickly.
U.S. Pat. No. 5,511,972 describes a partial combustion process in which the fuel is partially combusted using specific catalysts and catalytic structures and also a catalyst structure for use in the process. The catalyst structure is stable due to its comparatively low operating temperature, has a low temperature at which catalytic combustion begins, and yet is not susceptible to temperature “runaway”. The combustion gas produced by the catalytic process typically is below the autocombustive temperature for the gas mixture; the gas may be used at that temperature, or fed to other combustion stages for ultimate use in a gas turbine, furnace, boiler, or the like.